The operation of most agricultural vehicles requires substantial operational involvement and control by the operator. For example, in a combine the operator is required to control the direction and speed of the combine while also controlling the height of the combine head, the air flow through the combine cleaning fan, and the amount of harvested crop stored on the combine. Accordingly, to reduce the effort required by the operator, it is useful to automate as many tasks performed by the operator as possible.
One task which has been automated is the raising and lowering of the harvesting implement (head) of a combine when the combine approaches the headlands of a field. More specifically, some combines permit an operator to activate a switch monetarily for the purpose of causing the head to raise to a predetermined elevation without further interaction by the operator. Upon completion of a turn at the headlands and re-entry into the crop, the operator can activate another switch which causes the implement to return to its previous position for harvesting.
One of the main problems with prior systems for automatically raising and lowering harvesting heads at the headlands is the relatively slow speed at which the lowering occurs. More specifically, as the time required to lower a harvesting head to its harvesting position increases, the size of the headlands increases, and the amount of grain or other harvested material at the headlands lost due to failure to lower the head in a timely fashion also increases. Due to the nature of prior art control systems, relatively long time periods were required to lower harvesting heads to their operating position. For example, the prior systems typically controlled the operating height of a harvesting head based upon a sensor only capable of sensing the height when the head was relatively close to the ground. When the head was in the raise position during turning at the headlands, the height relative to the ground was not sensed.
Accordingly, the control systems moved the heads relatively slow until height relative to ground is sensed. In other words, the control system must operate open loop until height sensing of the head is initiated. As a result, the time required to lower the head to its operating position upon completion of a turn at the headlands is increased. Another reason prior systems have provided relatively long time periods for returning a harvesting head to its operating position is that they have typically been hydraulic control systems. To avoid incurring unacceptable costs in such systems by increasing the number of components, which thereby reduces the reliability in such systems, these systems have been made as simple as practical and, as a result, the speed at which the implements are moved while returning to their operating position is relatively slow.
In view of the prior art problems directed to returning a harvesting head to its operating position at the end of a turn at the headlands of a field, it would be advantageous to provide a system which reduces the return time by replacing hydraulic controls with electronic control, providing close loop control during the complete return process, and returning the head to its operating position at a speed related to the head's distance from the operating position.